(Solved) Coincell battery holder footprint


#1

Hi,

I was surfing the web looking footprints of coin cell battery holders to have ideas on how to design mine, and found this one here:

From an answer on that page:

The reason for the rectangular slots is to serve as thermal reliefs, similar to what is done for plated-through-holes. Without the slots, you would have to heat up the entire circle of copper before any solder would melt. And even then, the solder could flow over the entire area.

So the forced question is:
Is it possible to “recreate” the pad within a pad in KiCAD?
Any other design tips for footprints of battery holders?

Regards,
Carlos.


#2

I wouldn’t follow what Adafruit do, they often get things wrong. The answer on stackexchange is incorrect, thermal relief is only needed if you are using a point heat source (ie. soldering iron). During reflow all of the board is heated, so the answer is nonsense. Probably the real reason is to confine the solder to the central square. There is some good advice later on about surface finishes.

I would start again with the manufacturer’s data sheet and not worry about some weird stuff someone else has done.

Anyway, you can overlap multiple pads, but creating slots like that might be tricky.


#3

Instead of relying on second-hand information, it is better to look at the source. In this case, Adafruit publish their Eagle PCB and libraries files https://github.com/adafruit/Adafruit-Eagle-Library

Looking at their footprint :

You can see they have simple pads, but have defined a keep-out area on the solder mask (grey circle). So actually the thermal relief spokes are created normally by a zone fill on the board, it is nothing clever in the footprint. That might be easier to reproduce in Kicad.

For example

I created a circular pad on top of the square one, and set the solder mask clearance to 4mm.


#4

Thanks for the reply, I didn’t checked Adafruit footprint (I should had) but yes I was half sleep when realized that it’s just a keep-out zone and not a pad within a pad.
Will edit the post title and mark it as solved.
Thanks again :slight_smile:


#5

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